hello i also had ocd about my breathing, i know its very painful , since your mind will produce extreme doubts that what if you will forget breathing, what if you dont breath in your sleep etc, these all are due to ocd, actually you have to consult a psychiatrist for treatment of ocd, which includes medication and cognitive behaviour therapy, it will take time but you will get free from it
It is called sensorimotor OCD. here is a link if it is allowed on the site
http://beyondocd.org/expert-perspectives/articles/when-automatic-bodily-processes-become-conscious-how-to-disengage-from-sens
If not, then just Google Sensorimotor OCD.
I promise that you will not stop breathing. Breathing is a reflex action. Your body is going to do it whether you want it to or not.